Many communication systems, which often include wireless devices that both transmit and receive, operate in accordance with data transmission standards. Often, the data transmission standards specify relatively strict spectral mask requirements, which specify reduced amounts of noise, such as electromagnetic interference (EMI), during data transmission. The transmitter of such communication devices includes a power amplifier (PA) that is operable to transmit data in accordance with a data transmission standard. The PA typically receives power from a power converter, such as a DC-DC (direct current-to-direct current) converter. The power converter typically operates in a pulse-width modulation (PWM) mode during transmission in order to increase EMI compliance. The operating load on the power converter typically varies during operation of the communication device. For example, the operating load typically is relatively low while the system is in receive mode, during which time of operation the PA (and the power converter) is optionally turned off to conserve power. The power converter can be turned off because is normally inefficient to operate the power converter in a PWM mode during such times of low operating loads.
However, turning the power converter on again entails a relatively long wakeup time (e.g., on the order of hundreds of microseconds) during which the transmitter is not available for transmitting. The power converter can be switched to run in a relatively more efficient pulse-frequency modulation (PFM) mode during such low-load periods, but during the transition back to a PWM mode for a higher-load transmission period typically requires a settling time on the order of a few tens of microseconds. Such settling times exceed the settling requirements of some applications.